1. Field of the Invention
The present invention relates to an original cover closing device employed for closing an original cover for use in a copy machine, a printing machine, or the like.
2. Related Art
In recent years, moldings of synthetic resins (plastic) are used as parts in every industrial machinery. The synthetic resins have so-called creep characteristics such that (1) when a predetermined force is continuously applied, deformation is advanced with elapse of time, and even if the force is stopped, the molding is not returned to the original state, (2) when a predetermined deformation occurs continuously, its repulsion is decreased with elapse of time, and (3) when time is further elapsed, the molding is destroyed. Among the synthetic resins, since zircon (polyacetal copolymer) has excellent mechanical characteristics including a creep resistance characteristic, it is used in various fields.
Consequently, zircon is also used for an original cover closing device. The following device using zircon is known.
There is an original cover closing device comprising: a supporting member made of zircon attached to the device body side; a spring case provided integrally with the supporting member; a slider housed in the spring case slidably to a cam part; and compression means constructed by a compression spring compressedly provided between the slider and the bottom of the spring case so as to press the slider to the cam side.
The attaching member and the supporting member made of zircon can be produced cheaper than those produced by press working iron plates and have an advantage that the members can be made in various forms. Although zircon has a high creep resistance characteristic among synthetic resins, when the members are used for many years, the following problems occur. A crack occurs especially on the bottom of the spring case and the bottom is fell out. The spring case is broken when a force is applied and broken pieces spread, and the like.